She says six year-old Semeru was chosen because he fit all the necessary criteria.

“Firstly, he was the right age. Young male orangutans in the wild leave mum at about 7 years old.

“They have a very slow development and suckle for up to five years. In fact, the inter-birthing interval is the longest of any animal. In keeping with that, we separated Semeru from his Mum in April.

“We wanted him to be used to being away from his Mum as he would in the wild and he coped extremely well with this.”

In addition, Semeru showed early signs of independence, curiosity and good exploratory and foraging skills.

However, the Perth Zoo team needed to build on those attributes to prepare Semeru for his big change.

“At the beginning of the year we started him on different Indonesian foods and spoke to him in Indonesian, because that’s what the team will be speaking over there,” Ms Bullo says.

“We also used puzzle feeders and hoist baskets. Hoist feeders are on a pulley system so you can put food in them and then ‘hoist’ them 7-8m in the air. Semeru would have to hang from ropes and manipulate the food out of the basket.

Semeru was transferred to Indonesia in mid October where he will spend the next two weeks in quarantine, with the company of a Perth Zoo keeper.

The Indonesian Zoo team collect forest leaves and fruits for him to start recognising new foods, particularly a spiky palm called “rotan” which is highly nutritious.

Ms Bullo says the release date has been planned to coincide with the prime fruiting season so Semeru is released into the best conditions possible.

After he is released, there will be a tracking team monitoring his food intake and behaviour every two minutes.

“It’s a ‘soft release’. So we will also have extra food for him if he needs it,” Ms Bullo.

“It is also a gradual process that can take up to two years.”

Ms Bullo says the release is incredibly exciting for the keepers but also very hard work.

Semeru has been released into a protected Sumatran rainforest in a bid to bolster the endangered species.